For years, scientists have had evidence that Mars has harbored water. But the big question is did it play a big role in the planet's development, like it has on Earth? Could it have fostered life? John Mustard, a professor at Brown University, and his colleagues have used results from the Mars Reconnaissance Orbiter to provide, for the first time, an answer to these questions.

According to Mustard's results, water played an important role on Mars during the Noachian period, about 4.6 to 3.8 billion years ago. Mustard and his team investigated the presence of "phyllosilicates", clay-like minerals that show if water has interacted with rocks. By studying the phyllosilicate deposits in certain craters, valleys, and dunes, they have found that large regions of the ancient, southern highlands of Mars were water-rich in the past. There they found the clay-like minerals for the first time in sediments that were "clearly lain by water," Mustard wrote as lead author of the paper on the discovery.

The team found phyllosilicate deposits in thousands of places in and around the craters. "Water must have been creating minerals at depth to get the signatures we see," said Mustard. This observation agrees with the currently accepted theory that water was present about five kilometers below the ancient Martian surface. Then, the collisions that caused the craters sometimes brought it to the surface.

The phyllosilicates also provide a clue as to whether Mars was habitable during the Noachian period, since the clay minerals are formed at relatively "low" temperatures,that is 100 to 200 degrees Centigrade.

"What does this mean for habitability? It's very strong," Mustard said. "It wasn't this hot, boiling cauldron. It was a benign, water-rich environment for a long period of time."